* Shoulders: If you're talking about the front of an animal's body.
* Forelegs: If you're focusing on the front limbs.
* Head: If you're contrasting the lower part of the body with the upper.
* Upper body: If you're comparing the haunches to the overall upper region of the body.
* Slender: If you're talking about the physical shape, contrasting the bulk of the haunches.
Ultimately, the best antonym will depend on the specific context in which "haunches" is used.